This invention relates to the testing of integrated circuits, and more particularly to a method of fabricating a probe card apparatus for the testing of integrated circuits.
Integrated circuits (ICs) are formed as multiple, identical, discrete chips on a semiconductor crystal wafer. Each of the integrated circuit chips is usually tested to determine whether or not it functions as intended prior to cutting the wafer into individual chips. Typically, the chips are tested by computer operated test apparatus that exercises the circuits on the chips, using a testing process commonly referred to as multiprobe testing.
Conventional multiprobe testing employs a probe card which includes a plurality of electrical leads terminating in needles, which in turn make contact with input/output contacts of the various circuit elements on the integrated circuit chip being tested. The chip contacts most often are the pads to be electrically connected to the next level of circuitry, and are called bond pads. In the prior art, it is typical for probe cards to be built by attaching metal needles, such as tungsten to conductive traces on a polymeric ring. The needles or probe elements may be secured to the ring by an adhesive or they may be bonded, as by welding to a blade. An opening is provided in the center of the ring for the needles to extend through, and for aligning the needles to the bond pads. The card is positioned in a probe head which provides electrical connection to the controlling computer, and which mechanically brings the needles into contact with the bond pads on the chip.
The wafer support mechanism moves in and xe2x80x9cxxe2x80x9d and xe2x80x9cyxe2x80x9d direction in order to remove contamination, and make ohmic contact. The needles must all fall in the same place in order to assure that each one makes electrical contact with a contact or bond pad on the integrated circuit. This is accomplished by bending the needles after they are mounted on the probe card, which is laborious, time consuming, and expensive.
The close spacing necessary for testing some chips cannot be achieved with conventional needle contacts. In particular, needle contact probe cards are nearly impossible for high density bond pads on ICs where the pad pitch is 75 microns or less, and the density of contacts in the range of 400 or greater per device. The pitch of probe needles, and the angles of their projection necessary for these devices, are extremely difficult to manufacture, and in turn insures a high cost. Further, both delivery and maintenance of such cards adds significantly to the cycle time of testing. As a result of these issues, a number of attempts have been made to provide alternate probe card technology. Much of the newer technology centers around photolithographically defined conductor leads on polymeric membranes with plated or spring loaded contact mechanisms. Each of these approaches must have a means for applying uniform pressure to cause the membrane to make uniform contact across the chip. The issue of uniform contact, as well as alignment is aggravated by thermal expansion of the membrane because very often the chip generates a significant amount of heat during the testing procedure. Further, photolithography definition of the leads adds cost to the testing procedure, not only as a result of the initial cost and multiple steps involved, but also because new artwork and masks are required for each new device and/or change, thus adding to cycle time for production.
Thin film conductors have an added risk of increased inductance to the circuit, which is a significant issue for testing high speed devices. On the other hand, high resistivity of some probe needles, conductor traces, and multiple connections between needles, conductors on the probe card, and conductors to the probe head can also lead to inductance values which impact the accuracy of chip testing.
Because of the aforementioned issues with prior probe card technologies, and because of the anticipation of even tighter pitch of bond pads on integrated circuits of the future, it would be very advantageous for the industry to have a low cost probe contract apparatus, having a rapid means of fabrication, modification, or repair, having low inductance, and very high density of contacts.
It is an object of the current invention to provide a new and useful probe card contact apparatus which enables connection between a very high density of input/output pads on an integrated circuit chip, and more generously spaced contacts to conductive traces on a probe card of known technology.
It is also an object of the invention to provide a method for rapidly and economically manufacturing a high density probe card contact apparatus.
It is yet another object of the invention to provide a robust probe card contact apparatus which minimizes the amount of maintenance required during and after usage.
It is further an object of this invention to provide a probe card contact apparatus having thermal expansion similar to that of the semiconductor device to be tested so that contact is not compromised as a result of chip heating during testing.
It is an object of the invention to provide a probe card contact apparatus which is compatible with existing probe card technology, and multiprobe tester operation.
Yet another object of the current invention is to provide a reliable, high performance, probe card contact apparatus.
It is further an object of the invention to provide a reliable multipurpose contact apparatus.
The objectives of this invention are met by providing multiple, comb-shaped contact segments, each including a precisely positioned array of needles secured to a polymeric backing, and one or more of the segments positioned on a support block, which in turn is electrically and mechanically connected to a probe card. The needles are formed as integrally connected two-metal structures having tips of a noble or non-oxidizing metal, and fingers of an inexpensive readily available conductive metal. Rapid and low cost patterning of the needles and fingers is accomplished by a combination of chemical etching and high resolution laser processing.
The support block is a dielectric material having a low coefficient of thermal expansion which functions to secure the position of the probes, and to help control thermal expansion mismatches within the probing system, thereby minimizing movement of the probes relative to the chip during testing.
One or more comb-shaped segments of film are adhered to the semi-arc shaped surface of the support block, so that the noble metal needle tips which extend beyond, and are formed downward from the thin central portion of the block, can be brought into contact with the chip contact pads.
Terminals of the fanned out, common metal needle fingers extend onto the support block, and mate with contacts on a conventional printed circuit probe card. The support block is fitted into an opening in a probe card where the widely spaced fingers are connected to conductive traces on the probe card.
Precisely positioned needles are formed by patterning and etching a sheet of a two-metal composition, having one edge of a noble metal integrally attached to a less noble, conductive metal. High resolution, ease and low cost fabrication, and customized patterns are achieved by software input of the particular IC""s input/output pads, and the probe needle design into a fine beam laser for removing metal where the feature size is less than 100 microns. Patterning of features greater than 100 microns is achieved by photopatterning and chemically etching the two-metal structure.
In an alternate embodiment, a film of a laser ablatable material is deposited on the surface of the two-metal sheet, and the laser ablates a mask for subsequently patterning the and removing the excess metal from the two-metal sheet, and forming the needles. The fine beam of currently available lasers easily meets the tight pitch requirements of chip pads both in current production and those planned for the future.
Rapid response cycle time is achieved by assembling a few polymeric segments with probe needles onto a support block and fitting into a probe card, rather than attempting to align and assemble hundreds of probe needles on a card. Software input of design, coupled with laser processing is a significant factor in the ability to respond rapidly to the need for new probe cards designs, and the manufacture of high density, and/or high performance probe card apparatus. A two-metal needle structure combines highly reliable, noble metal tips with low cost fingers which may further be optimized for performance.
The foregoing and other objectives, features and advantages will become more apparent from the following detailed description of preferred embodiments of the invention which proceeds with reference to the accompanying drawings.